Makoy Samuel Yibi and his team from the Carter Center are on the brink of eradicating Guinea worm in South Sudan.
As the last remaining cases are being treated, the identification of a nomadic cattle herder with a Guinea worm in his foot is a cause for alarm.
The team has to figure out where the herder has travelled for a year previously in order to disinfect all sites he may have travelled through and make sure communities along the way are taking precautions against ingesting the Guinea worm from infected waters.
However the herder believes the worm was sent from the devil and wants to leave the camp where the team can treat his worm to slaughter a goat. He seems unwilling to give much information about where he has travelled.
If the team misses an infected water source, the devastating cycle of Guinea worm infection could re-emerge in communities close to eradicating this ancient neglected disease.
Learn more about this disease on the Lifelines Guinea worm homepage.
Watch the full film "How to Slay a Dragon".